Line circuit for automatic telephone systems



Patented Nov. 29, 1949 LINECIRCUIT FOR AUTQMATIG TELEPHONE.

SYST MLSI Winfred T. Powell, Rochester, N=.'Y.; assignorito Stromberg-Carlson Companxn-a corporation of New York pp ca on AP B rl Ni -13342 3 This invention relates to line circuits for automatic telephone systems-and more particularly to-such circuits comprising'only two relays.

It is an object of myinvention to provide a new and improved two-relay linecircuit for telephone systems.

In accordance with my invention there is provided a two-relay line circuit -includinga differentially wound two-coil line relay and a two- :winding slow-releasing 'cut-ofirelay. On originating calls, the line relay operates through one of its windings to causea finding operation. Upon seizure of the calling line by the line finder, the cut-off relay is operated-through one of its windings. Operation o'f the cut-off relay is employed to energize the-other'line relay winding to de-energize the line relay. on incoming calls, the cut-off relay is operated, the line-relay remaining mic-energized. n revertive calls, the relays operate as in outgoing calls except that when the link is released,- lock-out is achieved bymaintaining the cut-off relay-operated and reoperating the line relay through its operating winding.

Further objects and advantages of myinvention will be apparent'from the following description-and accompanying drawing which describe and illustrate, respective y, the, preferred form of my invention.

In the drawing there isillustrateda partyline lcomprising, for examplasubscribers stations land 3, line relay LR, cut-off relay CO and. switching apparatus such, as means for .findinga calling line represented by,the rectangle 4. and me pre ented b e t n l 'fom nn n a calling station located at ,anotherlocation (not shown) to the line .I.

As is evidentfrom an inspection ot the drawing, the complete line circuit includes only two relays, identifiedas alinenrelayanda cut-off relay. These two relaysrperform not-only the normal functions assigned to such relays, but also lockout functions.

outgoin cc If -it be assumed that-anindividual-wishes.to make a call from a station connected-to line] and has removed. the receiver to closethe-hook switch contacts at'that location, the tip and ring conductors T and R, respectively, of line I, are bridged to complete a circuit for operating line relay LR, the circuit extending from ground, through contact I of relayCO, lead T, the sub- Scribers substation, lead-R, contact 2 of relay CO, and the upper or operating winding of relay LR to battery. Line relay LR has two windings diljiercnti-allyarranged; One, illustrated as the upper, is-used tooperate the relay. The other, shown as the lower, is utilized to release the relay, the two 4 Claims. (Cl; Jig-P17 windings being connected in field opposing relationship.

The energization of relay LR grounds the units markinglead through contact I of relay LR and contact 5 ofrelayCOandgrounds the tens marking lead through contact-4 of relay LR and-contact l of relay '00; Operation of theline relay 1R:also grounds sleevelead 6 between the line circuit and connector 5 at'contact 3 of relay LR, therebyimmediatelymaking the line-busy to incoming calls. Closure of contact I of relay completes a locking connection for its upper winding overring lead R, subscribers loop, tip lead-'1 and contact I of relay CO to ground, such locking circuit being .ofv no useful purpose at this time.

'The fi-nding operation iscarried out toseize-the calling line by anysu-itable means known to the art. A complete finder is not shown, but 'for the purposes of this description, certain relays are shown and it is believed suflicient to note-that,

upon seizure of-the calling line after the finding aoperationis-complete, a calling relay GB is energized by extension of the tip and ring leads, T

iand R; respectively. Energization of relay 03 causes energizationof delay relay SAand operation ofarelay SA=-energizes a repeating relay SAP, over obvious.circuits.-

Energization-of relay SA. also grounds sleeve lead -':lextending-.between line and finder through contact I of-rrelayfiA; Ground on sleeve lead 1 energizes out+offrelay- 00- through its upper winding. closure-ofacontactt of relay CO energizes the lower or release winding of relay LR over a, circuit includinggrounded sleeve lead I, contact 30f ,relayCG);v contact 2'of relay LR and winding of "relay-LR to battery. Relay LR releases. Operation'of relay CO opens the marking leads. Cut-off relay CO remains operated because of the presence-of sleeve ground on one terminal oi'its upper winding andibattery on its other terminal. Grounded sleevelead I is connected to leadlithrough contact '5 of relay LR, following release .of relay LR; to prevent seizure of line l by any connecton Followingltermination of the call,'loss of ground onzsleeve lead-' 1 de.-energizes cut-ofi relay C0,a nd lined is ready-for'the next call.

lzzcomingcqll arcvertive cal smad the u nce escr bed n pnnection with. utgoi calls akes place until the busy signal is received.

Relay SA is maintained energized during the revertive call busy test and ringing period by suitable means, not shown, such as disclosed in my U. S. Patent 2,315,378, issued March 30, 1943 and assigned to the same assignee as the present invention. Accordingly, relay CO remains operated.

When the calling party hangs up upon hearing the busy signal there is caused the de-energization of relay CB in any Well known manner. After a time delay, relay SA releases to open the upper sleeve lead I, which de-energizes cut-off relay CO. Relay CO is slow to release, however, and before release takes place, a new energizing circuit is completed at make-before-break contact 2 of relay SA, through contacts of relay SAP, and lockout lead 8 to re-operate line relay .LR. Re-operation of relay LR completes a circuit for energizing relays LR and CO in series, the circuit extending from ground at contacts 4 and 5 of relay LR, lower winding of relay CO, tip lead, subscribers substation, ring lead, contact I of relay LR and upper winding of relay LR to battery. Talking current is thus furnished through the above mentioned windings in series.

LR, and CO and the consequent restoring of the line circuit to normal.

What I claim is:

1. In a telephone system having a plurality of lines, each line comprising a line circuit having only two relays, namely, a line relay and a cutoff relay; one of said lines having a plurality of substations; means for extending a call from or to any of said line circuits; means responsive to the presence of an outgoing call on a given line for causing operation of said line relay; switch ing apparatus; means controlled when said line relay is operated and said cutofi relay is unoperated for marking one of said lines as a calling line to said switching apparatus; means responsive to the seizure of said calling line by said switching apparatus when a call is thereon for causing operation of said cutofi relay; means responsive to the operation of said cutoif relay for causing the return of said line relay to its unoperated position; and means responsive to a reverting call condition on said one line for energizing in series the line relay and the cutofi relay associated with said one line in order to lock out said one line and to supply talking current to the substations involved when a connection is established therebetween.

2. In a telephone system, a line circuit for use by a subscriber, a line relay individual to said subscribers line circuit and having two differentially wound windings, means utilizing one of said windings for operating said line relay over said line circuit responsive to the removal of a receiver thereon to indicate a calling condition on the line, switching means responsive to said calling condition to extend a connection from said calling line circuit, a two-winding cut-01f relay, means utilizing one winding of said cut-ofi relay for operating said cut-01f relay over the extended connection, switching means responsive to operation of said cut-off relay for energizing the other winding of said line relay, whereby said line relay is de-energized to remove the calling condition from said line circuit.

3. In a telephone system, a line circuit for use by a subscriber, a line relay individual to said subscribers line circuit and having two differentially wound windings, means utilizing one of said windings for operating said line relay over said line circuit responsive to the removal of a receiver thereon to indicate a calling condition on the line, switching means responsive to said calling condition to extend a connection from said calling line circuit, a two-winding cut-01f relay, means utilizing one winding of said cut-off relay for operating said cut-oil relay over the extended connection, switching means responsive to operation of said cut-off relay for energizing the other winding of said line relay, whereby said line relay is tie-energized to remove the calling condition from said line circuit, and circuit means utilizing said one winding of said line relay and effective on reverting call service for reoperating said line relay, circuit means for de-energizing said one winding of said cut-off relay, and circuit means including said one of said windings of said line relay and the other of said windings of said cut-off relay in series for maintaining operated both of said relays for supplying talking current to substations when a connection is established therebetween.

4. In a telephone system, a line circuit for use by a subscriber, a line relay individual to said subscribers line circuit and having two differentially wound operating windings, means utilizing one of said windings for operating said line relay over said line circuit responsive to the removal of a receiver thereon to indicate a calling condition on the line, switching means responsive to said calling condition to extend a connection from said calling line circuit, a two-winding cut-ofi relay, means utilizing one winding of said cut-off relay for operating said cut-off relay over the extended connection, switching means responsive to operation of said cut-off relay for energizing the other winding of said line relay, whereby said line relay is de-energized to remove the calling condition from said line circuit, and circuit means utilizing said one winding of said line relay effective on reverting call service for reoperating said line relay, circuit means for de-energizing said one winding of said cutoff relay, and circuit means including said one of said windings of said line relay and the other of said windings of said cut-off relay in series for maintaining operated both of said relays for supplying talking current to substations for marking the line as a busy line when a connection is established therebetween.

WINFRED T. POWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,465,393 Goodrum Aug. 21, 1923 1,910,972 Stokely May 23, 1933 2,142,658 Saunders Jan. 3, 1939 2,199,543 lomax May 7, 1940 2,297,092 Wicks Sept. 29, 1942 2,314,933 Griflins Mar. 30, 1943 2,325,877 Powell Aug. 3, 1943 2,409,586 Powell Oct. 15, 1946 

